Misson impossible? Psh. Jack Littleworths(CaptainMonkeys) and me successfully walked in the cave and on the dock. The boat also had the green ring around it, but I don't know if it works or not, didn't try it. (Unfortunately though, we used the stair glitch and walk through wall glit ch to do it. ^^)
Let me upload the pics to xs.to and I'll post em. ^^
LARGE PICTURES, CONTINUE WITH CAUTION
The cave has been infiltrated

The dock, only the ramp connecting the two is fake. The dock is 100% solid.

The end, you can actually jump up to "Kingshead" from here

Oops, how'd our spy pic get here. ^^

Finally on the dock.
There is another way to do this, but I'd have to figure out how I did that stupid glitch where I was always in the water. ^^